High Temperature Distillation

vocabulary of the engineer specializing in distillation. Still others presented short cuts in methods for the solution of the equations that must be s...
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I CHEMICAL ENQlNEERlNO REVIEWS

OPERATIONS REVIEW

I

II High Temperature Distillation I

I

DURING

1956, persons interested in distillation continued to follow various interests in studying the divergent aspects of the operation. The usual studies in the fundamental data of vaporliquid equilibria are reported by several sources. Others presented the results of theoretical surveys into the control of operating equipment. Equilibration time, transients, sample points, and dead time became familiar terms in the vocabulary of the engineer specializing in distillation. Still others presented short cuts in methods for the solution of the equations that must be solved in theoretical consideration of distillation. New processing techniques including continuous reaction in a distillation column and continuous distillation of pine gum were presented. Many new tray designs have been presented during recent years. Most of these have a lower initial investment cost than the conventional bubble-cap tray. Sieve trays, slotted trays, and similar devices have their advocates. Most of these units perform excellently when used at the design condition, but they lack the inherent stability of the bubble-cap tray. The Uniflux tray offers the advantages of the bubble-cap tray and the economy of the newer designs. At the same time, new distilling apparatus for special purposes serve the particular needs of special industries. The Kuhn still for heavy water separations, and the hollow tube Turbogrid still for fatty acid distillations have been presented. The rotating core stills have again received attention. The modified rotating core still, known as the brush still, and used as a thermal distillation unit seems to be most promising. Liebman (7) reviews the history of distillation from the Dibicos of Cleopatra (not the famous queen but a first century female alchemist), the first recorded distillation apparatus to Michael Kraft’s book, “The American Distiller,” which appeared in 1804. The efficiency of distilling units has been studied by several groups in a n effort to understand the factors controlling the efficiency of bubble-cap trays. Results indicate that the time of contact between the vapor and the liquid is most important. Diffusion theory shows that this efficiency may be involved with the

size of vapor bubbles and the time necessary for material to diffuse to the interface. However, liquid mixing on the tray is also a factor in the over-all efficiency. No new concepts in theoretical calculations are presented this year. Modifications and elucidation of accepted calculation methods have been offered. Several charts or monographs to simplify the work of calculation again appeared this year. Design calculations are also simplified by the use of charts.

Distillation Processes Processing of chemicals frequently involves distillation problems. At times new techniques of operation arise from the needs of the process. Continuous reaction in distillation equipment is considered by Bleck (24. Pure products may be formed by removing and fractionating the product as it is formed. Reversible reactions involving two and three components are used to develop the calculation modifications required in designing the equipment for this process. Recovery of ethylene glycol from spent antifreeze solutions requires the distillation under vacuum of the glycol from a charge containing an excess of sodium hydroxide to control the acidity of the product. This process is reported by Glaser and Thodos (&I A). better product results from continuous distillation of pine gum. The process time of 5 minutes, rather than 1 hour as in the batch process, results in a more salable gum (3A). An extensive review of the problems associated with the distillation of fatty acids and an analysis of the still that has been proposed for this work are presented by Lee (9A). The recovery of nitric acid from nu-

clear plant raffinates is complicated by the presence of fluorides and chlorides. Arnold, Whitman, and Podlipec ( 7 A ) propose an evaporator and a fractionating column for handling this material. The tower efficiency is 54%. Vacuum operation is recommended in order to reduce corrosion of the equipment by lowering the operating temperature. A special tray design, in which heat may be added to or removed from a system being distilled, amounts to a Turbogrid tray having been built of hollow tubes instead of solid bars. Using Dowtherm as a heating medium, and the upper half of the tubes as heating surfaces, heat transfer coefficients of 20 B.t.u./(hour) (sq. ft.) X (” F.) were obtained, About 2.5 square feet of total heating surface per square foot off-tower cross section can be developed ( 4 4 ) . Fractionation during condensation may be preferred to conventional equipment when dealing with vapor mixtures having low dew points. Kent and Pigford (SA) discussed the aspects of this process. Pressure distillation may also be used for the same type of systems. Pressures up to 5 atm. are used in a copper still for concentrating dilute solutions of formaldehyde ( 5 A ) . Azeotropic distillation of the oxidation pl;oducts of the C1 to Cr hydrocarbons may be used to prepare petrochemicals (74. Operations such as the azeotropic distillation of methyl ethyl ketone with 1-hexane to remove the impurities from methyl ethyl ketone, followed by extraction with water, are discussed.

Column Control and Instrumentation The instrumentation of a distillation column is complicated by a delayed response of the column to changes in

T. J. WALSH received his B . 0 . E . (1 939) and h4.Ch.E. (1941 ) from Rensselaer Polytechnic hstitute and Ph.D. ( 1 948) from Case Institute of Technology, where he is professor of chemical engineering. Wabh is a consultant on process design for Glascote Products, Inc., and Thompson Products, Inc. He is chairman of Cleveland section of ACS and president of Cleveland Technical Societies Council. He received the first Junior Technical Award of the Cleveland Technical Societies Council and in 1956, the Award of Merit from the Chemical Prdession of Cleveland. VOL, 49, NO.

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PART II

MARCH 1957

503

Interest seems more in the direction of calculating vapor-liquid equilibria data than in obtaining additional data, but new methods of obtaining data are proposed.

the control point. In a pentane splitter, 8l/2 feet in diameter by 112 feet high having 50 trays, this delay has a dead time of 10 minutes before a change in composition is noticed at the sample point and another 20 minutes is necessary to complete the change in composition. These results are similar to those reported last year for an extractive distillation column. Berger and Short ( I B ) conclude that the speed of response to control action is limited by the volume of material on those trays which are included in the control loop. Rose and U'illiams (6B)in studying the behavior of a five-plate column on a four-unit REAC (Reeves electronic analog computer) analog computer also found that the best control is obtained when the sample point and the control valve are close together. Thus the conclusion must be drawn that samples for control purposes should be taken from the overhead product. When temperature measurement is not sensitive to composition changes, a new method of determining the composition is preferable to lowering the sample point. This work also indicates that derivative control is ineffective in achieving control stability whereas proportional control is generally effective. Further work on this same subject by b'illiams, Harnett, and Rose (7B) shows that condenser holdup is destabilized but reboiler holdup is stabilized in the control operation. Changes in feed rate can be handled by proportioning the boilup rate to the feed rate. Reflux temperature is of minor importance as long as the additional reflux introduced by heating the external reflux to the tower top temperature is a small part of the total reflux. A similar effect of holdup in the reflux lines of a batch still was reported by Pierce (4B). Here, the holdup was actually greater than the volume of one fraction to be produced from the still. This set the top temperature into oscillation as the lower boiling material was returned to the still as reflux. The time for a continuous still to reach equilibrium after a change in any condition is of interest to all plant operators. Although all factors affecting this time are not resolved, computer calculations indicate that it is a function of the demand being placed upon the col-

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umn. Thus, at one particular set of conditions when the unit is operating at maximum separating ability the equilibration time is extremely long. Slight deviation from this point shortens the time to equilibrium by several factors. Jackson and Pigford (3B) find this time proportional to the square of the number of plates in the column. The linearized correlations predict order of magnitude only for this calculation. Rose, Johnson, and Williams (5B) find the time is a function of the nature and magnitude of the upset. The equilibration time is longer when the upset requires greater separation from the column than when the separation required is less. Columns may some day be redesigned by present standards in order to shorten the time to equilibrium. The concept of a balanced column is introduced by Harbert (ZB). The balanced column produces a maximum purity of both products. Many times, present control systems prevent this. Harbert suggests several schemes for handling the two halves of the column as separate entities.

Fractionator Capacity and Design The prediction of the ability of distilling equipment to handle vapor and liquid loads at known pressure drop and efficiency is the goal of correlations for the design engineer. When combined with cost data, these predictions permit the proper selection of fractionating units. Swanton (27C) suggests a desirable way to specify columns so that the designer can meet any needs in the most advantageous manner. Bolles (3C) in a series of articles discusses the actual design of bubble-cap trays. Tray dynamics and standard designs are covered and a sequential procedure of design is suggested. A chart for rapid analysis of an existing tray, in terms of liquid and vapor handling capacity, is recommended by Walsh and Lafyatis (22C). Katzen (74C) compares trays as an aid in selecting the right one. Using the cost of the bubble-cap tray as 1.00, a Flexitray will cost 0.7, a UnifIex tray will cost 0.5, and a perforated tray will cost 0.7. Data on the Turbogrid trays are given but the cost range is not indicated.

INDUSTRIAL AND ENGINEERING CHEMISTRY

Details of design factors are evaluated by Lockhart ( I X ) who derived a formula for the drain time of bubble-caIi columns based on a modified orifice equation. The results fit experimental data within 7%. The important variables are the physical characteristics of the trays and the viscosity of the flowing liquid. The Davies equation for liquid gradient on trays is rewritten by Rodriguez (79C). The resulting equation is set up in nomograph form for ease in calculation. An unusual tray designed to satisfy unusual conditions involves the use of trays, only 4 inches apart, having 1-inch diameter bubble caps for fractionation in an ammonia plant. The heat pickup from the surroundings is important here; therefore, a minimum surface was desired. The close tray spacing resulted from the considered design. Small bubble caps were necessary to keep the slot vapor velocity to a low value (6C). The capacity factors of sieve trays were investigated by Hunt, Hanson, and Wilke (77C). Hole diameters were equal to the plate thickness. Plates having holes, 3- or 4-hole diameters apart, were stable while those having holes only 2 diameters apart were unstable (possible exception is 1/8-inch holes). The pressure drop was greater in all cases than the sum of the pressure drop through the dry hole plus the head of liquid on the tray. I n evaluating the liquid film efficiencies of sieve trays, Foss and Gerster (QC) found that the tray performance depends upon the total gas throughput rather than the velocity through the perforations. As with bubble caps, the number of transfer units was proportional to the nominal time of contact between the liquid and the vapor. The product of the linear gas velocity and of the square root of gas density ( F factor) is found to be a correlating variable for column efficiency in the studies of the American Institute Chemical Engineers, Plate Efficiency Research Committee (IC). According to Oliver and Watson (77C) the efficiency of a tray is intermediate between that predicted by Murphree and by Lewis. Because of the mixing on the tray, the slot velocity is more important than the superficial velocity, and higher liquid depth and higher pressures give higher efficiency.

The latter effect may be due to the lower viscosity of the liquid resulting from the higher temperature of the boiling liquid. The effect of pressure on plate efficiency for a 30-plate column, 600-mm. diameter, is reported by Marek and Novosad ( 76C). Entrainment, however, was not affected by the number of slots in the work of Atteridg and others (2C). The caps used were the Kellogg rectangular type. The entrainment increased with a decrease in liquid path length and with closer cap spacing. The effect of liquid rate varied in this study. Geometric design of plates and capacity was also studied by Cervenka and Cerny (5C). Packed columns were also studied. The use of short packed sections is suggested by Edye (8C). Several sections, each 60-mm. highin a 25-mm. diameter column, were studied. Sizmann and Stuhe (20C) report the effect of inert gas on the individual phase resistances. Several packings are compared by Capitani and Milani (4C). Jacobs (72C)presents a nomograph for the determination of the diameter, pressure drop, and allowable velocity of a packed column. Rotating concentric core columns show excellent efficiency under the proper conditions. A column, 50 inches long and 4.5 inches in diameter with a 0.032inch clearance, showed as many as 120 theoretical plates at 5000 r.p.m., 3.4 moles per hour throughput, and atmospheric pressure. However, a t 200 mm. of mercury absolute pressure, this still showed only 35 theoretical plates (70C). A modified rotating core still which is also a modified thermal distillation still is the brush still (78C). In this still the cooled central core carries a continuous spiral wire brush. The bristles are long enough to reach the heated outer wall. The still works best with no top reflux and is most effective in separating materials of high molecular weight. The wet-walled still may be used for fractionation of close-boiling liquids. The Kuhn column consists of a bundle of open tubes maintained at a constant temperature by a vapor jacket. Cronan (7C) indicates that 400 theoretical plates have been obtained with one of these units. Janolik (73C)describes a versatile apparatus for distillation using direct heat, steam, vacuum, inert gas, or air as a carrier.

Calculations Methods of making distillation calculations may be varied in several ways depending on the calculator and the data of the problem. Fisher (40)combines a weight per cent per mole per cent conversion chart with the conventional McCabe-Thiele diagram. Voorwijk (70) presents a circular nomograph for the solution of equations similar to y =

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Ax/l+ ( A 1)x. A modification of Underwood’s equations has been developed by Klein and Hanson (5D). General calculation methods are set up by Adolphi and Fleischer (ZD),while Boyd (30) indicates the modifications necessary in multidrawn columns. The relationship between distillation and other operations is made clearer by the work of Vener (6D). Acrivos and Amundson ( 7 0 ) continue to develop calculation procedures. Part 111 discusses numerical solutions of improper integrals, Part IV-minimum reflux ratio, Part V-packed columns, and Part VI-the extension to nonideal cascades. laboratory Equipment Miniature Hyper-Car, spinning band, and concentric tube columns were studied at total and partial reflux by Nerheim and Dinerstein (6E). The HyperCal unit has a lower height equivalent to a theoretical plate but the spinning band column has lower holdup and pressure drop. These studies reveal the importance of holdup. The spinning band column gave the best separation of small samples, although the Hyper-Cal unit had the greatest number of theoretical plates. An integrated set of laboratory fractionators in five sizes from 1 to 80 liters is described by Cooke and Jameson

7E). Microstills, in which 0.8 to I-ml. portions of oil may be distilled with results that compare with the accepted specification distillations and fractionators for 5-ml. samples yielding cuts that correspond with those from crude oil assays using several liters, are described by Javes, Liddell, and Thomas (5E). The columns are packed with l/ls-inch Dixon nickel cylinders. Another small equilibrium still having a charge capacity of 40 ml. is described by Ellis and Thwaites (2%). Fiberglas textile packings are proposed by Hala. Vilum, and Fried

(3E). Porous glass may be used to prevent bumping in distillation flasks (4E). The shape of the porous surface depends upon the desired pressure. A double-walled vessel may be used for the distillation of flammable liquids (8E). A new still head is described by Riley (7E). Testing of laboratory columns may be done with a dilute solution of thiophene in benzene (9E). Analysis is colorimetric. Another approach is to use radioactive trace material. Sulfur 35 was proposed.

Vapor-liquid Equilibria Although several articles appeared during the year, interest seems to be more in the direction of calculating data than in obtaining additional data. Spin-

ner and others (27F)propose empirical equations for the prediction of binary vapor-liquid equilibria data for a system using basic data information for the compounds involved when present in other binary systems, and for prediction of ternary equilibria using data on two of the three binary systems. Jaffe (70F) discusses the effect of temperature on the composition and pressure of azeotropes. He proposes a method of calculation based on van Laar equations but not restricted to constant values of the van Laar coefficients. Kharbanda (75F)extends the usual evaluations to partially miscible systems. Rao and Krushnamurty (25F)give an equation based upon the Gibbs-Duheim relationship for checking the consistency of teknary data. Binary azeotropes of paraffin hydrocarbons with fluorochemicals and of cvcloparaffins with fluorochemicals were reported by Mair (27F). The cycloparaffin containing azeotrope has a lower boiling point than the equivalent paraffin azeotrope. Three- and four-component azeotropes in toluene-isobutyl alcohol-hydrocarbon-water systems were studied by Kominek-Szczepanik (77F). A graphical method of determining azeotropic composition is described by Kaiser (77F). It compares in accuracy with other methods and is faster to use. Hinshaw (7F)presents a correlation of t b vapor-liquid equilibria constants for hydrocarbons. Kay and Albert (73F) extend this knowledge of how these constants depend upon the environment, The equilibrium constants of ethane in cyclohexane are intermediate between those of ethane in paraffinic and aromatic liquids. Last year, this review indicated that data of Hipkin and Myers (8F) do not indicate azeotropes in aliphatic-aromatic systems. These data are now available from the American Documentation Institute for study by those working with these systems. Further data by Myers (23F) on naphthene-aromatic systems shows considerable deviations from ideality for cyclopentane-benzene, methylcyclohexane-benzene, cyclohexanetoluene, and methylcyclopentane-toluene, but no azeotrope is formed. An azeotrope is formed in the methylcyclopentanebenzene system. Weber (28F) reports that the systems 2,2,5-trimethylhexaneethylbenzene and 1-octene-ethylbenzene deviate only slightly from ideal behavior. Acetic acid was an ingredient in several studies of equilibria. The acetic acid-water system is analyzed thermodynamically by Kivenc (76F)and azeotropes of acetic acid-paraffins are reported by Kurtyka (ZOF). Diketeneacetic acid and diketene-acetic anhydride were investigated by Dinaburg and Porai-Koshets (6F). Marek (22F) discusses the effect of association on eqriilibria in binary systems containing acetic

VOL. 49,

NO. 3, PART A

MARCH 1957

505

UNIT

OPERATIONS REVIEW

acid. Ternary systems of acetic acid, 2.6-lutidene, and paraffins were investigated by Zieborak and others (29F). Methods of determining vapor-liquid equilibria are reviewed by Ridgeway (?SF). New techniques are proposed by Kranich and others (78F), who suggest continuous sampling of rhe vapor and the liquid samples, and by Kiimmerle (79F), who also suggests recirculation of both the liquid and the vapor. Another new still is suggested by Katz and Newman (72F). These authors tested the still with the ethanol-l-heptane system. The data correlate with a four-suffix van Laar equation. The Benedict equation of state did not satisfactorily correlate vapor-liquid data for the systems propane-carbon monoxide or propane-carbon dioxide according to Cullen and Kobe ( 5 F ) . Other interesting binary data for nitromethanebenzene and for nitromethane-carbon tetrachloride are reported by Brown and Smith (2F). Ternary systems received much attention. This may imply that researchers have passed to more difficult studies in the equilibria field leaving the binary systems to be investigated by those with an interest in a particular system. All binary systems and the ternary are reported for acetone-benzeneethylene dichloride by Canjar and others (4F), for methanol-ethanol-acetone by Amer and others (7F), for ethane-ethylene-acetylene by Hogan and others ( 9 F ) , for butanol-butyl acetate-water by Pick and Fried (24F), for phenol-acetylchloride-water by Byk and Scherbak (3F), and for ethanol-benzophenone-water and ethanol-triphenyl carbinol-water by Khairulina (747).

Bibliography (1 ) Liebman, A. J., J.Chem. Educ. 33, 166 (1956).

Distillation Processes (1A) Arnold, D. S., M’hitman, A , Podlipec, F. J., Chem. Eng. Progr. 52, 362 (1956). (2A) Bleck, L. H., .4.I.Ch.E. Journal 1, 467 (1955). (3.4) Chem. Eng. 63, 132 (June 1956). (4A) Cronan, C. S., Chen. Eng. 63, 238 [Julv 1956’1. Farbeiov, i f . I., Speranskyaya, V. A , J . Appl. Chem. (U.S.S.R.) 28, 205 (1955). Glaser, M. B., Thodos, G., Chem. Erg. Progr. 52, 95-M (1956). Hopkins, Ft’. C., Fritsch, J. J., Petroleum Processine 10, 1217 11955). Kent, E. R., Pigford, R.’L.. A.?.Ch.E. Journal 2. 363 (1956) (9.4) Lee, C. A.,’Chem. Eng. 63, 189 (July 1956).

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Column Control and Instrumentation (1B) Berger, D. E., Short, G. R., IND. END.CHEM.48, 1027 (1956).

506

Harbert, W. D., Petroleum Rejiner 35, No. 11, 151 (1956). Jackson, R. F., Pigford, R. L. IND.EKD.CHEM.48, 1020 (1956). Pierce, D. E., Ibid., 48, No. 9, 51A (1956).

Rose, .4.,Johnson, C. L., Williams, T. J.. 16id.. 48. 1173 11956). (6B) Rose, .k, Williams, T.‘ J., h i d . , 47, 2285 (1955).

(7B) Williams, T. J., Harnett, R. T. Rose, A., Ibid., 48, 1008 (1956).

Fractionator Capacity and Design (1C) .4m. Inst. Chem. Engrs., Distillation Research Committee, Annual Progress report, 68 p., 1955. (2Cj Atteridg, P. T., Ixmieux, E. J., others, A.I.Ch.E. Journal 2, 3 (1956). (3C) Bolles, LV. L., Petroleum Processing 11, S o . 2, 64; No. 3, 82; No. 4, 72; No. 5, 109 (1956). (Reprints available from Fritz-Glitsch Inc., Dallas, Tex.). (4C) Capitani, C., Milani, E., Chimica e industria (Milan)37, 932 (1955). (5C) Cervenka, M., Cerny, O., C h m . Priimysl5, 232 (1955). (6C) Chem. Ene. 63. 132 IMar. 1956). ( 7 c j Cronan,“C. S , , ChEm. Eng. 6 3 , 246 (October 1956). (8C) Edye, E., Chem. Eng. Technol. 27, 651 (1955). (9C) Foss, A. S., Gerster, J. A , , Chem. Eng. Progr. 52, 28-5 (1956). (10C) Hawkins. J . E., Burris. W. A., Anal. Chem. 28,.1715 (1956). (11C) Hunt. C. d’A.. Hanson. D. N.. LViike, C. R., “4.I.Ch.E . ’Journal 1, 441 (1955). (12C) Jacobs, J. K., Petroleum Refiner 35, KO. 6, 187 (1956). (13C) Janolik, J., Chem. Zvesti 9, 188 (1955). (14C) Katzen,’ R., Cheni. En?. 62, 209 [November 1955). i15C) Lockhart, F, J., Pelroleurn Refiner 35, No. 11, 165 (1956). (16’3 Marek, J., Novosad, Z., Chem. Lisfy 50, 337 (1956). (17C) Oliver, E. D., Watson, C. C . , A.I.Ch.E. Journal 2, 19 (1956). (18C) Perrv. E. S.. Cox. D. S.. ISD. ENG. c&. 48,’1473(1956j. (19C) Rodriguez, F., Chem. Eng. 63, 230 (November 1956). (20C) Sizmann, R., Stuhe, B., Chem. Enp. Technol. 27, 669 (1955). (21C) Swanton, W.F., Petroleum Refiner 35, No. 10, 113 (1956). (22C) Walsh, T. J., Lafyatis, P., Chern. Eng. 63, 193 (April 1956). I

Calculations (1D) Acrivos, A,, ;imundson, N. R., ChPm. Ene. Sci. 4. Part 111, 141: Part IV; 159; Part V, 206; Part VI, 249 (1955). (2D) . , AdolDhi. G.. Fleischer. R., Chem. fech.‘ (Berlin) 7, 638 (1955). (3D) Boyd, C. W., OzIGas J.53, No. 52,72 (1955). (4D) Fisher, R. W., Chem. Eng. 63, 234 (August 1956). (5D) Klein, G., Hanson, D. N., Chem. Eng. Sci. 4, 229 (1955). (6D) Vener, R. E., Chem. Eng. 63, 175 (August 1956). (7D) Voorwijk, J. F., Ibid., 63, 201 (May 1956).

INDUSTRIAL AND ENGINEERING CHEMISTRY

Laboratory Equipment Cooke, G. XI., Jameson, B. G., Chem. 27, 1798 (1955).

Ellis, S. R. M., Thwaites, J.

Chem. e Procrss Eng. 36, (1955). Hala, E., Vilum, P. J., Fried Chem. Lisly 49, 359 (1955). Iida, T,, Anal. Chem. 28. 1213 ( 1 Javes, A. R., Liddell, ’ C , , Thomas, W.H., Ibzd., 27, 931 (1955). Nerheim, 4. G., Dinerstein, R. .\., Ibzd., 28, 1029 (1956). Riley, F. T., Chernzstry hdurtry 1955, p. 940. Smith, C . C . , .Vature 175, 1136 (1955). Zvel’benskii,Va. D., Shalygin, V. .\., Seftjanoe Kho:. 33, No. 8 , 65 (1955).

Vapor-liquid Equilibria (1F) Xmer, H. H., Paxton, R. K., Van Winkle, hf., IND.END.C H m . 48, 142 11956). Smit F., Australian J , Brown,’ I., Smith, Chem. 88,, 501 (1955). (I Byk, S., Scherbak, Scherb L., Zhur. Fiz. Khim. 30, 56 (1956). (1 Caniar, L. N., Horni, E. C., .It.., Rbthhs, R. R.. IND.ENG.C H F M . 48, 427 ’( 1956).‘ Cullen, E. J., Kobr, K. A, d.I.Ch.E. Journal 1,452 (1955).

Dinaburg, ’ M. M - ‘S,, S., Porai-Koshets, B. A . , J . Appl. Chem. (1,’A’S.R.) 28, 517 (1955).

Hinshaw, D. F., Univ. Microfilms Pub. 12,587 (Univ. of Mich., Ann Arbor, Mich.). Mich.), 1955. Hipkin, H., H . , Myers, H. S., IKD.ENG. CHEM.46. 11954). 46, 2525 (1954). Hogan, R. j Neisdn, J.,., Nelson, iV:-T., W.T., others, 16id., 47, 2210 (1955j. Jaffe, J., Ibid., 47, 2533 (1955).

Kaiser, L., Compt. rend. 242, 132 /,nci\

(1956). {IYJU).

Katz, K., Ncwman, hl., M., ISD. Er\c;. Ex(;. CHEM.48, 137 (1956). Kay, W. B., Albert, R. E., Ibid., 48,

422 (1956). (14F) Khaidina, ’K. K., Zhur. Obshchei. Khim. 25, 2427 (1955). ( l 5 F ) Kharbanda, 0. P., Chem. Process Eng. 36, 245 (1955). (16F) . . Kivenc, G., Mtm. services chim. i f a t (Pari;) 38, 311 (1953). (17F) Kominek-Szczepanik, M., Roctuiki Chem. 29, 783 (1955). (18F) Kranich, W. L., Wagner, R. I;., others, IND.END. CHEM.48, 956 (1956). (19F) Kummerle, K., Chem.-Ing.-Tech. 28, 400 (1956). (20Fj Kurtyka, Z., Bull. acad. polymer x i . , Classe 111, 3, 47 (1955). (21F) Mair,B.J.,Anal.Chern.28,;2(195(i). (22P) Marek, J., Collection Czechoslou. Chem. Comms. 20, 1490 (1955). 48, (23F) Sfyers, H. S., Irn. END.CHEM. 1104 (1956). (24F) Pick, J., Fried, V., Chem. Listy 49, 1112 (1955). (25F) Rao, C., Krushnamurty, V., ~ J Sci. . Ind. Research f~ India) 15B. 44 , (1 956 ’). , (26F) Ridgeway, K., Ind. Chemist 32, 59 (1956). ( 2 7 ~ Spinner,' ) I. H., ~ u B., C. Y . , (;raydon, W.F., IND.ENG.Cnui. 48, 147 (1956). (28F) Weber, J. H., Ibid., 48. 134 11956). (29F) Zieborak, K.. others,’Roczniki (,‘hem. 29, 783 (1955).